The present invention relates to manually operated circuit breakers and, more particularly, to circuit breakers having a moveable contact on a spring biased contact member manually actuated through a toggle arrangement.
Circuit breakers, providing reuseable electrical circuit protection, have gradually replaced fuses providing one time protection, in most applications throughout the United States. These circuit breakers consist of a fixed electrical contact to which one circuit conductor is connected and a moveable contact to which the other circuit conductor is connected. A handle is exteriorly provided for manual operation of the breaker between open and closed circuit conditions, corresponding to separation or engagement of the moveable contact and the stationary contact, respectively. The handle is connected to the moveable contact through a toggle arrangement such as an over-center linkage. It is imperative that the engagement of the stationary and moveable contacts occur with sufficient pressure therebetween to avoid destruction of the contact material as a result of arcing therebetween. In order to maintain firm contact between the moveable and stationary contacts when the circuit breaker is in the closed condition, the toggle mechanism maintains considerable force on the moveable contact against the stationary contact.
Circuit breakers include a mechanism for sensing overcurrent conditions when the contacts are conducting more electrical current than the breaker is rated to carry. While any one of a number of mechanisms may be incorporated within a particular circuit breaker, the mechanism often comprises a magnetic or bimetallic releasable latch which enables automatic opening of the breaker in the event that the current carried thereby exceeds a predetermined value. When the circuit breaker is to open as a result of the releasable latch functioning, it is desirable that the physical opening of the contacts occur at as rapid a rate as possible. To obtain the rapid movement of the moveable contact relative to the stationary contact, mechanical mechanisms such as springs are provided between the stationary and moveable contacts. Obviously, the opening of the circuit breaker will occur at a speed dependent upon the force of the biasing spring provided between the contacts.
It may be easily understood that the operation of this biasing or push-off spring, and the toggle mechanism for forcing the contacts against each other when the breaker is closed, may actually impede one another. Additionally, the force of any mechanism biasing the contacts apart for the purpose of providing quick opening of the circuit breaker, directly opposes the force necessary to manually operate the breaker into a closed condition. As a result, increasing the biasing pressure between the contacts normally increases the pressure required in order to move the circuit breaker handle from the open position to the closed position. Various attempts have been made at constructing a manually operated circuit breaker which provides sufficient force against the stationary contact by the moveable contact when the breaker is intended to be in the closed position, which provides adequate biasing between the contacts to enable quick opening of the breaker upon release by a latch mechanism and which enables ease of operation from the open condition to the closed condition by movement of the toggle handle. Examples of breakers which address all of these problems are illustrated in U.S. Pat. No. 3,581,261 and 3,610,856. In each case, the apparatuses disclosed in the above mentioned patents include an additional spring providing the force required to cause the breaker to open quickly upon release by the latching mechanism.